New data shows a worrying trend: Baltimore harbor’s health is in decline

Despite decades of work to clean up Baltimore’s harbor and restore its habitat for fish and underwater life, new data suggests a concerning trend: water quality is getting steadily worse.

Testing sites across the harbor — an area that stretches from downtown to the Middle Branch — ranged from “poor” to “fair,” according to 2025 water quality data published Wednesday by the nonprofit Blue Water Baltimore.

Alice Volpitta, Blue Water’s harbor water quality watchdog, said that more than a decade of monitoring by her organization suggests that concentrations of phosphorous, an oxygen-depleting nutrient, are on track to deplete the harbor ecosystem further in the years ahead.

“We can talk all day long about whether ‘fair’ is good enough for the residents of Baltimore,” Volpitta said. But “we have to start thinking: ‘Is this good for the next generation, or the generation after that?’”

Exactly what’s driving this trend remains something of a mystery, but Volpitta said it shows how much more needs to be done to curb runoff from urban stormwater. Blue Water’s annual report showed a similar trend a year ago, and Volpitta said changes from year-to-year are small.

Even so, the results come on the heels of a rough stretch for the Baltimore harbor.

Persistent rains last summer dashed plans for the second Harbor Splash event, when some 200 people were registered to jump into the water in Fells Point. As weather cooled at the end of summer, thousands of fish turned up dead in the water while the harbor took on a sickly green shade that lasted for weeks.

Known locally as a “pistachio tide,” harbor scientists believe this event was triggered by weather conditions but made worse by decades of harbor pollution. Last year’s event, which persisted for weeks in September and October, was the longest of its kind in recent memory.

Blue Water has monitored water quality in the Baltimore harbor since 2013. The group’s report focuses on the health of the harbor ecosystem — for underwater life like fish, crabs and plants — but Volpitta said the news about the water’s safety for human recreation is brighter.

Levels of harmful bacteria like enterococcus have improved steadily, a sign that efforts to control sewage pollution are paying off. Baltimore’s Department of Public Works has operated under consent decrees to fix its wastewater treatment plants and end sewage overflows, which still contaminate city waterways during heavy rains. The department projects that it will have spent more than $2 billion on system improvements by the end of the decade.

Adam Lindquist, the vice president of the Waterfront Partnership, is one of Baltimore’s most vocal advocates for a swimmable harbor. His organization plans to bring back organized swims this summer — this time staging events on multiple days — and Lindquist thinks the harbor could soon have a permanent swimming area.

The improving bacteria scores are an encouraging sign for this dream, Lindquist said, but he stressed the importance of turning around the ecosystem health, too.

While reviving the Patapasco’s ecosystem has proven frustrating, testing stations in the streams that flow into the harbor show more encouraging results.

Other factors like climate change and increased rainfall, however, could exacerbate the harbor’s challenges.

Volpitta said the harbor’s middling scores are driven largely by the growing concentration of phosphorous, a nutrient that can drive algal blooms that sap oxygen. What’s driving this phosphorous trend isn’t clear, but she speculated that warming waters may be triggering the release of dormant phosphorous pollution at the bottom of the harbor.

“There are processes at work here that we don’t fully understand,” Volpitta said, “but our data is starting to unlock the fuller picture.”